Electrography



Au 4, 1953 J. P. EBERT 2,647,464

ELECTROGRAPHY Filed Oct. 26, 1949 3 Sheets-Sheet 1 FIGURE FIGURE 2 INVEN TOR. Jo mes P. Ebert RM W M AGENTS J. P. EBERT ELECTROGRAPHY Aug. 4,1953 3 Sheets-Sheet 2 Filed Oct. 26, 1949 FIGURE 4 FIGURE 5 INVENTOR.James P. Ebert AGENTS.

Aug. 4, 1953 J. P. EBERT 2,647,464

ELECTROGRAPHY Filed Oct. 26, 1949 3 Sheets-Sheet 3 FIGURE 7 FIGURE 6 INV EN TOR. Jo mes P. Ebert BY v A a AGENTS.

Patented Aug. 4, 1953 ELECTROGRAPHY James P. Ebert, Columbus, Ohio,assignor, by mesne assignments, to Battelle Development Corporation,Columbus, Ohio, a corporation of Delaware Application October 26, 1949,Serial No. 123,651

21 Claims. (Cl. 101-426) This invention relates to an electrical methodfor reproducing printed images and other images and to apparatus foreffecting such electrical reproduction.

Various methods for reproducing images printed on paper or otherwisesuperimposed on various materials have recently been proposed anddeveloped. For example, U. S. Patent No. 2,297,691 to Chester F. Carlsondescribes an electrophotographic method for obtaining images onconductive plates having a photosensitive or photoconductive layer ofmaterial applied thereto.

It is an important object of this invention to provide means and methodsfor reproducing images without requiring the use of photosensitivelayers of materials, whereby the step of light exposure may beeliminated in image reproduction.

It is another object of this invention to provide means and methods forreproducing either side of material having images on both sides by asimple contact procedure.

Yet another object of this invention is to provide a new and readilyapplicable method for preparing master plates for duplication andprinting processes.

Other objects and advantages of this invention will be apparent in viewof the following description thereof, considered in the light of theattached drawings wherein,

Figure 1 shows several methods of preparing a plate for use in theprocess of the invention,

Figure 2 is a cross-section through a plate suitable for use in thepresent method,

Figure 3 is a view showing an assembly of the various elements inposition for the preliminary steps of the process, and

Figure 4 illustrates one method of producing a latent electrostaticimage of the material to be reproduced on an electrographic plate,

Figure 5 illustrates a way of developing, or making visible, such latentelectrostatic image,

Figure 6 illustrates the accumulation of powder particles on the imageareas, and

Figure 7 illustrates one of the transfer methods for transferring thedeveloped powder image to paper or other transfer material.

Essentially the present invention relates to a process of imagereproduction wherein an electrostatic image of the image to bereproduced is prepared on a plate coated with a dielectric material.

A basic element in the present process is a plate upon which the imageto be reproduced is first reproduced in the form of an electrostaticimage and later caused to take on a physically visible form bydeveloping with a suitable powder. Such a plate comprises a backingplaten of metal or other suitable electrically conductive material and alayer of a dielectric material over the surface of such backing platen.Such plates are hereinafter designated as electrographic plates. Manymethods for applying the layer of dielectric material to the metal platehave been de vised and there is nothing critical in the method ofapplication. The dielectric layer is preferably between 0.00025 and0.0005-inch thick although thicknesses as great as 0.002-inch areoperative. Examples of methods which have been successfully employed inthe application of the dielectric v materials include:

trically conducting plate.

(3) The dielectric material may be deposited upon an electricallyconductive plate by vacuum evaporation.

(4) One side of a commercially prepared plastic film may be coated byvacuum evaporation with a metallic substance which is a good electricalconductor.

(5) Other miscellaneous methods such as dipping the plate in a solutionof the dielectric material or flowing the solution over the plate andremoving the excess by scraping with a metal or wooden blade, etc, mayalso'be used in the preparation of electrographic plates.

Once the 'electrographic plate has been prepared as above described itis ready for repeated use in the process as hereinafter set forth.Briefly the steps of this process may be stated as follows:

'1. The original to be copied is placed so that the image to bereproduced is in contact with the dielectric layer of the electrographicplate. (See Figure 3.)

2. An electrostatic charge is applied to the dielectric surface throughthe original being copied. This may be accomplished by corona dischargefrom wires or needles, or by induction for example.

3. The original which is being copied is stripped from the plate.

4. The electrographio plate is contacted by an electrically chargedpowder. This results in the production of a visible powder image of thelat ent electrostatic image formed in step 2. In this step the powdershould have the same polarity of charge as the charge applied to thedielectric surface in step 2.

5. The developed powder image istransferred to a second surface bysuitable electrical, me-

chanical, or chemical process.

6. The transferred image is permanentlyfixed to the second surface. Thismay conveniently be accomplished by heating; or by chemical'zfixing, orother similar processes.

'7. The electrographic plate is=-cleaned* of-any-- remaining powderparticles and is discharged of any electrostatic chargesr. remaining:rthereon. This is readily accomplished by scrubbing the plate surfacewith a damp rag and permitting the plate to dry, for example. The stepsdescribed. above are illustrated. in the v drawings, wherein,

Figure l illustrates-"several:ways in-whiclnthe *dielectriclayersmaybeapplied to a: backing plate. In (a) is shown a:top;view of arotating device l2 to which is fastened aplate I-3 to: becoatedt-Theplate i3 is fastened to:the;whirling or rotating device I2by:any-tsuitable; fastening means (not shown) l A dielectric-materialwhich -has-been dissolved in .asolvent is represented: at I5." Itwill=be seen :thatzuponrotating l2; the dielectricm-ateriat I5- will becaused to flow and -cover the entire area of. plate [3; evenly;andtuni--formly. In (1)) it isillustrated-how aplate l3 can-begiven a coatingof.dielectric material by spraying thedis'solved dielectric l5 from aspray device l6, shown schematically.':.ln '(C) a vacuum ---evaporatio'ntechnique is illustrated." Plate 13 is suspended by wires [4- 441 withina: vacuum chamber l-l wherein -a:dielectric material-held in a containeris vaporized;bythe -.applicationi of --heat- :supp1ied;-for-:example;-by a;-rresistance heater coil *device [9 energized.= zthrough= rleads22- -22. The entire-assembly issupporte'd'by a suitablebench orltable23, as indicated.

In Figure 2 a crossesection-.throughfianelec- --trographic plate isshownto:illustrate that: such plates-consist oftwolayers;-first,;a:;dieleotric layer 2|, and, second, a backing layerof metal or mother :conductive material.

1* Figure 3 1 illustrates the iinitialstep in the process, wherein theoriginal 'copyj32 tobe'reproduced is placed with the material tobe-icopiedinicon- -.--tact= with the-.-dielectric layer 3.1 ofi anelectrowgraphic plate; 33cconsisting of. dielectric 3l;-;and wmetalbacking; 39.

iFigure i showsamethod of producingtaneelec- -trostatic-r charge:pattern" on: the. :electrographic plate wherein plate- 40;. with copy.4| bOzbBTBIJI'O- -.-duced-.pr.operly placed thereonras shown in Fi ure3, is passedvundencorona:dischargei'wires i- 43:.43- .energizedbyhighvoltagesource 44:; The wcorona. wires 4Si'43:.-are :strung betweenmetal bars 4545 supported by posts 4646 of wood,

- Trplastic or other non-conductive material, which,

" in turnymayrestupon or befastened to and sup- 'ported by. plate41;1P1ate' 4'1 -may be either a conductive or non-conductive material;If 'coninductive it should; be-r'grounded'electrically, if

- non-conductive, it will-:be necessary to-provide a.

-:,-;:ground .connectionforplate 49, as illustrated,

figure 5illustratesoneway of carrying. out the step of developing thelatent electrostaticiimage produced,onnanzelecuographic;plate by. theoperation shown in Figure 4. =;;Ani:elect1'ographic;

plate 50 which has a latent electrostatic image on its dielectric faceis placed in a tray 5|, provided with stops 52-52 to position plate 50.A

developer material 54 is caused to flow back and 5 forth across thedielectric face of plate 50 (by tilting tray 5| first one Way and thenthe other) :inwhereupon theeelectrostatic image is made visible byreason of the adherence of the developer material 54 thereto. In thedrawing the delo- 'veloper material 54 has been permitted to flow.-.1par.t;way across the face of plate 50 making visible those portionsof the image area 55 contacted zvrby the-developer. 54.

Fig'ure 6 illustrates the manner in which the l5-developer-- particles54 accumulate on the image areas 55 of the plate 50 during thedeveloping jij process; This figure shows a section through theapparatus of Figure 5 along the line 66. As --indicated in Figure 5, theparticles 54 have not 20 yet been cascaded entirely across the plate 50,and: most of theseparticles are still in the .upper -corner oftray 5l.l:However', itisialready: ap- -=-parent thatthe particles 54 arebuilding.up; in

the image area 55, while in the neighboring :nonzs' image areas, as-156,there is no accumulation of particles.

nc-transfer method for'transferringra developed image from anelectrographic plate. to a transfer :material is: illustrated in Figure7. .Itzmwill 30-be-.-noted that the same equipment-shown inFig- :ure 4may be used for the .transf.er.s tep,;.Intransferring, :plate. 6!).bearing; the: powder. .image:and

a transfer material, such as paper sheet Share passed: under-.coronaidischarge wires 431-:43 as 35 in the-chargingeten. .Note, however; thatthe-polarity of .the corona .wires; 43%43 is required to-be opposite in.thewtransfer step from what itrwas in the. chargingsstep. i .-.Thus,-.:as illustrated: where the corona discharge wires 43-43 are positive 40during. the :sensitizing process; they must beineg- .-.ative during .thetransfer... :Similarly, if the-corotjha zwires 43%43. are negative. in.the' charging or sensitizing step, they. must betpositive to.;efl'ect*;transfer.

1 It willbezunderstood that for 'certain; applica- .ztionsofithe'present process thedevelopedimage may be fused to theelectrographic plate instead ofaxbeing transferredto a secondsurface. asde- -'::scribed instep 5... Suchrapplications are:.con-

.cernedrwith' processeswhereina number of .duplications or copiesofflthe originalaredesired. The c :electrographic plateziwith theimage.fused theretormayiberaiscd in thezmanner of a master-plate insuchprocesses.

55 The methodabove. descrihedihas been-employed .:.in.;ma-king'copiesof'manykinds of original subjeots including thograph oicopyclndiaink drawings, pencil drawings, typewritten copy; mimeograph opy,endamany types. of:printedcopy.

Theseoriginals'may: be-thought of as stencils,- or

better electric-stencils?in:the present process. 3-, As a-matter offact, astencil made-by cutting a pattern to: be --printed into anelectrically: in- .sulatingor. electrically conducting material will 55serve as an original for the process.

There are many satisfactory dielectric coating .materialsand a-Jist ofthese would include the following: chlorinated rubber, Amberol F-71,

.Staybelite- Ester a? 10, polystyrene,- polyethylene,

Vinyl VU 1900,.Pliof1lm, ethyl cellulose,various combinations of.Parlonand-Rezyl, certain resin ItblEhdS made up of 7 variouscombinations ofzthe above-named resins, anthracene, and various 1 Ether;materials which possess-dielectric proper- ;..ies.

While the exact mechanism by which the pres ent invention operates isnot known or established, the following explanation is now generallyaccepted and is believed to possess considerable merit. The theorysupposes that to insure optimum operation of the invention both theoriginal to be copied and the electrographic plate to be used shouldmeet certain requirements and specifications. Broadly it appears thatthe original to be copied must comprise an image-supporting materialwhich is neither a good electrical insulator nor a good electricalconductor, and an image which has either a somewhat higher or a somewhatlower electrical resistance than the image-supporting material. In otherwords, it appears that the image-supporting material and the actualimage material must have at least slight differences in electricalresistance properties, if optimum performance of the method is to beobtained. Other factors probably contribute to the effect; for example,it appears that a thin layer of dielectric material of high resistivityon an electrically conductive backing produces superior results.

It is believed that when an original of either of the types mentionedabove is placed upon an electrographic plate of the type describedheretofore and subjected to an electrical discharge as previouslystipulated, those areas of the electrographic plate directly below thebackground portions of the original become more highly charged thanthose areas directly below the image portions. Consequently, anelectrostatic image of the original is formed on the electrographicplate in the form of an electrostatic pattern of varying chargeintensity. This electrostatic image is made visibile by applying anelectrically charged powdered material to the plate. This powder shouldbe electrically charged with electricity of the same polarity as theelectricity applied by the electrostatic discharge operation and is,therefore, repelled from areas of high charge intensity, and isdeposited upon the areas of low charge intensity, which are the imageareas. Experience has shown that this is always the case no matterwhether the original copy consisted of a conductive image on aninsulating background or an insulating image on a conductive background.Once the powder image is developed on the electrographic plate it may betreated in any one of several ways depending upon the ultimate use towhich it is to be put. For example, as previously pointed out, in oneapplicaiton the image is fused to the electrographic plate. Otherapplications require that the image be transferred to a second surfaceand this is conveniently done by placing the transfer material over theimage and spraying said transfer material with electricity of polarityopposite to the polarity of the electricity on the powder. Othertransfer methods may be used, of course. For example, various chemicaltransfer methods or methods involving hygroscopic action are available.

Whatever may be the exact mechanism by which the present method effectsreproduction of images, it is certain that the adoption of the stepsdescribed above will result in such reproduction in a rapid andsatisfactory manner. The following example shows the specific operationscarried out in preparing reproductions of either (1) images moreconductive than the supporting medium or (2) images less conductive thanthe supporting medium. Of course, it will be understood that thisexample has been selected 6 for illustrative purposes only and is notintended to be considered restrictive in any way.

Example An electrographic plate was prepared by the "whirling techniquepreviously described. In this manner a coating of Staybelite Ester #10(a glycerine esterified rosin manufactured by the Hercules PowderCompany, Wilmington, Delaware) was applied to an aluminum sheet. Thesolvent used was trichlorethylene and the whirling process required 5minutes of whirling at 40 R. P. M. The aluminum surface had previouslybeen cleaned by swabbing with acetone and cotton followed by a rinsewith acetone.

The coated plate was charged negatively by a corona discharge deviceoperating at 7000 volts (peak) half-wave rectified A.-C. The chargingwires were spaced -inch from the plate, and the plate was passed onceunder the discharge device at a speed of 1% inches per second. It isunderstood, of course, that the image to be reproduced was in contactwith the dielectric layer of the plate during the charging operation.

The electrostatic image produced by the abovedescribed charging processwas developed using a developer mixture wherein the powder componentconsisted of 20 parts Amberol F-71 (The Resinous Products & ChemicalCompany, Philadelphia, Pennsylvania) and 1 part Raven Bead Carbon Black(Benney 8: Smith Company, New York, N. Y.), integrally bonded together.The carrier component consisted of soybean protein.

The developed image was transferred from the electrographic plate to atransfer paper by the electrical method previously described andillustrated in Figure 7, employing positive corona discharge at 7000volts (peak) rectified A. C. The transferred image was fixed and madepermanent by heating on a hot-plate for a few seconds. The plate wascleaned and readied for re-use by wiping with a damp cloth.

The above-described procedure was followed in detail in reproducing boththe conductive-image and the insulating-image type original. It is alsopossible to use positive electrostatic discharge in sensitizing theplate, provided an appropriate developer combination is selected.

One of the striking features of the present in vention is that itpermits the reproduction of copy printed or drawn on both sides ofapaper by an electrical contact procedure without employing or involvingany light-sensitive elements. To do this it is necessary only to followthe steps already defined and to make certain that the side bearing theimage to be reproduced is placed in contact with the dielectric layerwhile applying the electrostatic charge. When the electrostatic image soformed is developed it will be found that the desired image has beenreproduced without trace of the image on the other side of the originalpaper from which the copy was made.

In the step of developing the electrostatic image it has been found thatvarious resinous powders are very satisfactory. These powders should becaused to assume an electric charge of the same polarity as the polarityof the charge on the electrographic plates. This may be done by means ofdevices which spray electric charges or may be effected by triboelectricaction in a mixture of the developer powder and a carrier material, theparticular materials chosen being determined and selected in accordancewith a triboelectric series, wherein it may be ascertained that thedeveloper ace-7,464.-

component will assume the proper' polarity"- tact with: any materialbelowit' in the series. A'

primary function of the: carrier material is to insure that thedeveloper powder'assumes the proper electrostatic charge polarity (bycontact withthe carrier). Additional data as to the properties andspecifications'of developerrmaterials-and carrier'particles" areincluded in 00- pendi-ng"applicationsaserial'No. 24,674, filed May 1,1948, by L. E. Walkup andE. N. Wise, and. Serial No.55,645,.filedz0ctober 20, 1948., by L. E. Walkup, now PatentNo.2,618,551. The particular powders and carriers used in the presentmethod are not criticalto its operation, the only requirement being thatthe powder be charged with the same polarity as the electrographicplate; In this connectionit should be noted that the image developingpowder. may be, and often is, of the same-materialaszthe dielectriclayer on the electrographic plate. Also in many cases the developerpowder consists of two or more components integrally bonded together.

The particular apparatus or technique employed in formingtheel'ectrostatic image on electrographic plates' is' not: critical andmany variations in: design and application are possible. Methods whichcan and have been used include producingacorona; discharge from wires orneedles and passing the electrographic plate through the dischargearea;v induction, as by covr1;

ering: the electrographic plate-copy assembly with a metal plate: and:connecting the metal plate to a. voltage source; andother methods ofproducing an electric field; in the vicinity of the plate-copy assembly.

In the electrographic. reproduction; of images which are made up ofmaterial which is more conductive: than the image-supporting material,it has been found that escape paths should preferably be providedfor'the electrical charges which arise on these areas during the.charging step. Such escape paths are sometimes inherent in thedielectric layer of the electrographic plate in the form of impuritiesor imperfections.

When notinherent in the plate they may be provided either by treatmentof the electrographic plate orliy treatment. of the-original copy- Forexample, small holes may be made in the dielectric layer of the plate,or'the image areasof the original copy may be connected together with anelectrical conducting material.

It will be appreciated theta new and useful method for reproducing copyhas been described. Throughout the specification and claims the word;copy is used to describe material to be reproduced. It will be readilyunderstood that the term, so used, is broad enough to include originalsto be copied as well as actual copy material' to be. recopied. It isagain pointed out for purposes of emphasis that no light-sensitiveelements are required and no light sensitizing steps are performed. Theoperation is based entirely upon electrical principles as has alreadybeen pointed out and explained. It will be apparent that the presentmethod provides for the production of either a positive or negative ofthe copy being reproduced. This is so. since the operation of the novelsteps is to produce charged areas corresponding to the non-image areasof the original and areas having little'or nocharge ISU which correspondtetheimageareas ofthe: original; By selecting a developer carrying acharge of.

the required polarity either the charged areas or the non-charged'areascan be developed, thus producinga positive orv negative copy as desired,and without regardto whether the original wasa positive or a negative.

What is claimed is:

1. An electric method of reproducing copy, comprisingthe steps ofplacing the copy to be re.- produced in contact with the dielectriclayer of an electrographic plate comprising a conductive backingplate'with a dielectric coating layer, subjecting such assembly to anelectrostatic discharge, removing the'original copy from theelectrograp-hic plate, contacting the plate with an.

electrically charged powder, transferring the powder image-so formed toa second surface, and fixing the transferred image to said secondsurface.

2. An electric method of reproducing copy, comprising the steps ofplacing the copy to be reproduced so that the image contacts thedielectric layer of an electrographic platecomprising aconductivebacking plate with a dielectric coating layer, subjecting suchassembly to an.elec-- trostatic discharge, removing the original copyfrom the electrographic plate, contacting said plate with a powderelectrically charged with the polarity as the polarity of the discharge,transferring the powder image so. formed to a secend surface, fixing thetransferred image to said second surface, and cleaning and-dischargingthe electrographic plate.

An electric method of reproducing copy, comprising the steps ofpreparing an electrographic plate consisting of a dielectric-layer on aconductive backing plate, placing the copy to be reproduced so that theimage contacts said dielectric layer, subjecting such assembly to anelectrostatic discharge, removing the original copy from theelectrographic plate, flowing a. powder electrically charged with thesame polarity as the polarity of the electrostatic discharge across saidplate, transferring the powder image so formed to a second surface, andfixing the transferred image to said second surface.

4. An electric method of reproducing copy, comprising the steps ofplacing the copy to be reproduced so that the image contacts thedielectric layer of an electrographic plate comprising a conductivebacking plate with a dielectric coating layer; subjecting such assemblyto an electro static; discharge, removing the original copy from theelectrographic plate, contacting said plate with a powder electricallycharged with the same. polarity as the polarity of the electrostaticdischarge, electrostatically transferring the powder image so formed toa'second surface, and fixing the transferred image to said secondsurface.

5. An electric method of reproducing copy, comprising the steps ofpreparing an electrographic plate consisting of a dielectric layer on aconductive. backing plate, placing the copy to be reproduced so that theimage contacts said dielectric layer, subjecting such assembly to coronadischarge, removing the original copy from the electrographic plate,contacting said plate with a powder electrically charged with the samepolarity as the corona discharge, electrostatically transferring thepowder image so formed to asecond surface, and fixing the transferredimage by heat to said second surface.

6. An electric method of'reproducing copy, com prising the steps ofpreparing an electrographic plate consisting of a dielectric layer on aconductive backing plate, placing the copy to be reproduced so that theimage contacts said dielectric layer, subjecting such assembly to anelectrostatic discharge, removing the original copy from theelectrographic plate, flowing a powder electrically charged with thesame polarity as the polarity of the electrostatic discharge across saidplate, transferring the powder image so formed to a second surface,fixing the transferred image to said second surface, and cleaning anddis charging the electrographic plate with a damp cloth.

7. An electric method of reproducing copy, comprising the steps ofplacing a copy comprising an image-supporting material and an imagematerial of different electrical conductivity properties in contact withthe dielectric layer of an ,electrographic plate consisting of adielectric coating layer on a conduitive backin plate, sub- J'ectingsuch assembly to an. electrostatic discharge, removing the copy from theelectrographic plate, contacting said plate with a powder electricallycharged with the same polarity as the polarity of the electrostaticdischarge, transferring the powder image so formed to a second surface,and fixing the transferred image to said second surface.

8. An electric method of reproducing copy, comprising the steps ofpreparing an electrographic plate consisting of a dielectric layer on aconductive backing p1ate, placing the copy to be reproduced so thatthe-image contacts said dielectric layer, subjecting such assembly to anelectrostatic discharge, removing the original copy from theelectrographic plate, contacting said plate with a powder electricallycharged with the same polarity as the polarity of the electrostaticdischarge, and fixing the image so formed to the electrographic plate.

9. An electric method of reproducing engineering drawings, comprisingthe steps of placing the drawing to be reproduced so that thedrawnimage'contacts the dielectric layer of an electrographic plateconsisting of a dielectric coating layer on-a conductive backing plate,subjecting such assembly to an electrostatic discharge, removing thedrawing from the electrographic plate, flowing a powder electricallycharged with the same polarity as the polarity of the electrostaticdischarge across said plate, transferring the powder image thus formedto a second surface, and fixing the transferred image to said secondsurface.

10. An electric method of reproducing either side of copy printed onboth sides, comprising the steps of placing the side of the copy desiredto be reproduced in contact with the dielectric layer of anelectrographic plate consisting of a dielectric coating layer on aconductive backing plate, subjecting such assembly to an electrostaticdischarge, removing the copy from the electrographic plate, contactingsaid plate with a powder electrically charged with the same polarity asthe polarity of the electrostatic discharge, transferring the powderimage thus formed to a second surface, and fixing said transferred imageto said second surface.

11. An electric method of reproducing copy, comprising the steps ofpreparing an electrographic plate consisting of a dielectric layer0.00025 to 0.0005-inch thick on a conductive backing plate, placing thecopy to be reproduced so that the image contacts said dielectric layer,subjecting such assembly to an electrostatic discharge, removing theoriginal copy from the electrographic plate, flowing a powderelectrically charged with the same polarity as the polarity of theelectrostatic discharge across said plate, transferring the powder imageso formed to a second surface, and fixing the transferred image to saidsecond surface.

12. An electric method of reproducing copy, comprising the steps ofpreparing an electrographic plate consisting of a dielectric layer lessthan 0.002-inch thick on a conductive backing plate, placing the copy tobe reproduced so that the image contacts said dielectric layer,subjecting such assembly to an electrostatic discharge, removing theoriginal copy from the electrographic plate, flowing a powderelectrically charged with the same polarity as the polarity of theelectrostatic discharge across said plate,

transferring the powder image so formed to a second surface, and fixingthe transferred image to said second surface.

13. An electrical method of reproducing an image formed upon a materialhaving a different electrical resistance from said image, comprising thesteps of bringing the image bearing material into contiguous relationwith the dielectric layer of an electrographic plate comprising adielectric coating layer on a conductive backing plate, and subjectingsaid contactingimage bearing material and dielectric layer to anelectrical discharge, thereby to form an electrostatic image of saiddesign on said dielectric layer.

14. An electrical method of reproducing an image formed upon one side ofsheet material having a different electrical resistance from said image,comprising the steps of bringing the image bearing side of saidmaterialinto face to face contact with the dielectric layer of anelectro graphic plate comprising a dielectric coating layer on aconductive backing plate, and imposing an electric charge upon saiddielectric face through said sheet material, thereby to form anelectrostatic image upon the dielectric layer of rial having a difierentelectrical resistance from said image and having a second image formedupon a second parallel surface of said material on the opposite side ofsaid material from said first surface, comprising the steps of bringingthe first surface of said image bearing material into contiguousrelation with the dielectric layer of electrographic plate comprising adielectric coating layer on a conductive backing plate, and subjectingsaid contacting image bearing material and dielectric layer to anelectrical discharge to form an electrostatic image of the image on thefirst surface on said dielectric material.

16. An electrical method of reproducing an image formed upon a materialhaving a diiTerent electrical resistance from said image, comprising thesteps of bringing the image bearing material into contiguous relationwith a dielectric layer adhered to an electrically conductive plate,subjecting said contacting dielectric layer and image bearing materialto an electrical discharge to form an electrostatic image of said imageon said dielectric layer, removing the image bearing material from saiddielectric layer, and bringing said dielectric layer into contact with afinely divided electrostatically attractable material thereby to makevisible said electrostatic image.

17. An electrical method of copying an image formed upon a surfacehaving a different electril l cal resistance from said image upon adielectric layer-adhering to an electrically conductive plate,comprising the steps of bringing the image bearing surface into contactwith said dielectric material, subjecting said contacting image bearingI surface and dielectric layer to an electrical discharge to form anelectrostatic image of said image on said dielectric layer, removing theimage bearing surface from said dielectric layer,

bringing said dielectric layer into contact with a finely dividedelectrostatically attractable material thereby to form a transferableimage, and subjecting-said transferable image and said second surface toan electrical discharge thereby to transfer said image from saiddielectric layer to said second surface.

18. An electrical method of copying an image formed upon a surfacehaving a different electrical resistance from said image comprising thesteps of bringing the image bearing surface into contact with thedielectric layer'of an electrographic plate comprising a dielectriccoating layer on a-conductive backing plate, subjecting said contactingimage bearing surface-and dielectric layer'to an electrical discharge toform an electrostatic image of said image on said dielectric'layer,removing the image bearing surface from said dielectric layer, bringingsaid-dielectric'layer into contact'with-a finely divided elec--trostaticallyattractable material thereby to form I a transferableimage on said layer corresponding to the image to be copied, andtransferring said image on to a secondsurface.

19. An electrical method-of copying an image formed upon asurface havingdifferent electrical resistance fromsaid image, comprising the steps ofbringing theimage bearing surface into contact with the "dielectriclayer of an electrographic plate "comprising a "dielectric coatinglayer-on a conductive backing plate, subjecting said contacting imagebearing surface and dielectric layer to an electrical discharge to forman electrostatic image of said image on said dielectric layer, removingthe image bearing surface from said dielectric layer, bringing'thesai'ddielectric layer into contact-with afinely divided 'electrostaticallyattractable material thereby to form a transferable image on said layercorresponding to the'image to b'e copied, transferring "layer 'on aconductive backing plate, subjecting said contacting image bearingsurface and dielectric layer to an electrical discharge to form anelectrostatic image of said image on said dielectric layer, removing theimage bearingsur-face from said dielectric layer, bringing saiddielectric layer into contact with a :finely divided electrostaticallyattractable material thereby to form a transferable image on said layercorresponding to the image to be copied, bringing a secondsurface 'intocontact with said transferable image, subfleeting-said transferableimage and said second surface to an electrical discharge thereby totransfer'said image from said dielectric layer to said second surface,and fixing said transferred image to said-second surface.

21. In an electric method'of reproducing copy wherein an electrostaticimage of the copy is produced; on an electrographic plateconsisting ofan insulating coating on a conductive backing, the

steps comprising exposing the plate to an electrostatic dischargethrough the copy while the copy is in contact with the plate, andremoving said .copyfrom said plate.

JAMES P. EBERT.

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